The subject matter to which this invention pertains is in the field of fasteners. Bolts and screws are used in a wide variety of aerospace and aircraft applications to secure and attach components that feature at least one coplanar surface. In these applications, it is generally desirable to apply a predetermined torque to a bolt, whereby a state of tension exists state of compression exists in the fastened members. The typical bolt may feature a length of threads starting from the end opposite the head of the bolt and extending along the shaft of the bolt, the threads terminating at the shank of the bolt. The length of the shank, or smooth unthreaded portion of the shaft of the bolt between the threads and the head of the bolt, is defined as the grip length, or grip, in design vernacular. The shank is also typically where the maximum shear strength of the bolt is developed because of the larger, uninterrupted net section area in this region, as opposed to the broken surface of the threaded portion. Consequently, it is undesirable to place the threads of the bolt in the shear plane between two fastened surfaces because of the reduced strength of the bolt in the threaded region. Therefore, ensuring that the bolt shank is located and passes through the shear plane of any fastened members attains significant advantage. In addition, where the thread/shank interface of the bolt terminates at or extend slightly beyond the combined dimension of the two fastened members, there is a risk that a nut threaded onto the bolt will not sufficiently compress the two members together. Where this situation occurs, there is a temptation of a maintenance worker or fabricator to continue rotating the nut/bolt combination beyond the thread/shank interface of the bolt in an effort to tighten the joint. This may result in the bolt/nut being partially or fully stripped, with subsequent weakening the joint.
Presently, fastener systems that require the maximum bolt shear strength and the maximum member bearing strength, such as aircraft and aerospace applications, tend to need washers or shims place beneath the bolt and nut head to locate the bolt shank at the desired depth in the joint. Where a washer cannot fit within the confines of the joint, a special washer must be fabricated or the bolt strength must be compromised. In other cases, governing specifications that require the use of certain types and classes of bolts may limit the availability of thread length and grip length combinations. In these cases, the grip length of the bolt may exceed the joint thickness, in turn causing the bolt threads to terminate at the nut before the opposing members contact or before the appropriate compression can be applied to the joint members. The result can be normal and lateral movement between the members, which in turn reduces the quality of the joint.
Accordingly, it is one object of the invention to provide a general solution to this problem by allowing the thread/shank interface portion of the bolt to extend beyond the members to be joined to insure that the shank of the bolt is fully present at the shear plane between these members and that the appropriate amount of compression may be applied to the joint members. This is accomplished by providing additional thread between the bolt shank and the nut whereby the shank of the bolt is allowed to extend through the contact plane of the joined members, ensuring that the full shear strength of the bolt is attained and the appropriate amount of compression may be applied to the adjoining members.